T₃/T₄ Ratios and α-Glycerophosphate Activity in Intact Rats Exposed to a Cold Environment

Abstract

The quantitative distribution of I-containing compounds has been studied in the thyroid and different tissues of intact rats, equilibrated isotopically with I¹²⁵ and exposed to 4-10°C for two weeks. It was found that the T₃/T₄ ratio was increased in extrathyroidal samples. The T₃/T₄ ratio in the intrathyroidal pool of "free" iodothyronines also tended to increase. In the liver, but not in the kidney, of cold-exposed rats, the concentrations of T₃ was higher, and the concentration of T₄ the same, or lower. The α-GPD activity increased in the liver, but not in the kidney of similarly treated animals. A positive correlation was found between α-GPD activity and T₃ concentration, but not between α-GPD and the concentration of T₄. These and previous findings support the idea that conversion of T₄ to T₃ plays an important role in the expression of a biological effect of T₄.

Thyroxine - Triiodothyronine - α-GPD - Cold- Exposure - Rats - Isotopic Equilibrium